Biology 4410
Quiz questions
Cytoskeleton and Cell Signaling
A. Cytoskeleton Questions (2 qp each)
1. A scientist wishes to detect the location in a living cell of a protein known to be present at
low concentration. What technique would make the structure easily visible and easily
seen in a living cell?
2. How can the rate of movement generated by molecular motors be measured?
3. How can genetic mutations be used to determine cytoskeletal function?
4. Why would the addition of an irreversibly binding ATP analog to an in vitro system for
monitoring molecular motors stop motor function
5. A scientist observes the motion of a certain type of vesicle around the cell. She notices
that vesicle movement ceases when colchicine is added to the culture medium. What
conclusion can she draw?
6. In an electron micrograph, an object is visible in cross-section. It appears to be made of
nine sets of three hollow tubes that are fused together. They are arranged in a pattern that
looks much like a pinwheel. Next to this object is a similar object oriented
perpendicularly to it. What is the object in the micrograph?
7. A scientist is observing a dividing cell. For a few minutes, he steps away from his
microscope, which is fitted with a device to maintain the cell being observed at 37°C.
The thermostat on his device malfunctions and the temperature of the cell drops to about
4°C. He is unable to see the spindle when he returns - why?
8. If complete axonemes are placed in a test tube in the presence of an antibody that
recognizes the globular heads of the dynein arms, what would happen when ATP is
added to the medium?
9. Phalloidin, a chemical found in poisonous mushrooms, stabilizes microfilament structure.
Usually, stabilization is considered to be a good thing. Why is it a problem in this case?
10. A cell containing actin filaments, intermediate filaments and microtubules is treated with
heavy meromyosin (HMM) or the smaller S1 subfragment that can be visualized in the
electron microscope. Which filaments, if any, are decorated with HMM or S1? Is the
decoration orderly or are the decorations randomly distributed?
11. Just as a cell enters Prophase of mitosis, you treat it with cytochalasin B. Will the cell be
likely to proceed to Anaphase? What will happen if you add cytochalasin B just as
cytokinesis begins?
12. You discover a mutant mouse whose skeletal muscles do not work properly. You excise
muscle tissue in an attempt to discover the problem. The only abnormal thing you can
find is the lowered affinity of the muscle for binding Ca2+ ions. Thus, the initiation of
muscle contraction is more difficult. What is the muscle protein that is most likely to be
affected by this mutation?
13. You are observing the movement of vesicles in a squid giant axon. The vesicles are
moving from the cell body toward the synaptic terminal. What is the most likely
molecular motor involved?
14. What microtubule-related microscopic abnormality might be seen in the brains of people
who have died of Alzheimer's Disease (AD)?
B.
Cell signaling questions
1.
Succinylcholine is a chemical analog of acetylcholine. It is used by surgeons as a
muscle relaxant because it produces a type of flaccid paralysis by blocking the
nerve impulse at motor neuron end plates.
(a)
If succinylcholine is a chemical analog of acetylcholine, why do you think it
causes muscles to relax and not contract as acetylcholine does? In your answer,
you must relate your explanation specifically to the process of cell-cell signaling
that takes place at the motor neuron end plates. Also, suggest an experiment to
test your hypothesis. (A hint and note: this question has nothing to do with actin
and myosin. Keep it simple and don’t get sidetracked.) (5 qp)
(b)
Care must be taken in the use of succinylcholine because some individuals have
an adverse reaction. In most cases, the patient recovers from the succinylcholine
paralysis after a short time. In cases with sensitive patients, the individual
recovers abnormally slowly from the drug, with life-threatening consequences. It
is known that abnormal sensitivity to this drug can be inherited. Considering that
it is an analog of acetylcholine, suggest a molecular explanation of the sensitivity
to succinylcholine in sensitive patients. If your explanation is correct, then how
could a physician treat a sensitive patient to whom succinylcholine has been
accidentally administered? (5 qp)
2.
(This is the one I mentioned in class. Adapted from Wilson and Hunt, Molecular
Biology of the Cell: The Problems Book)
Drosophila larvae molt in response to an increase in the concentration of a steroid
hormone called ecdysone. The polytene chromosomes of the Drosophila salivary
glands are an excellent experimental system in which to study the patterns of gene
activity initiated by the hormone, because active genes enlarge into puffs that are
visible under the light microscope. Furthermore, the size of a puff is proportional
to the rate at which it is being transcribed.
The diagrams show the results of three different experiments to investigate the
role of ecdysone in regulating transcription in Drosophila. In these experiments,
the salivary glands were dissected from live Drosophila larvae. At time 0,
ecdysone was added to the dissected glands, and changes in the pattern of puffing
were observed over a twelve hour period. The curves shows the sizes of three
different chromosomal puff regions (on different regions of the chromosome).
The three puff regions are called “intermolt,” “early,” and “late.” The differences
between the three experiments are as follows:
Experiment (A) shows the normal response of Drosophila
puffs to ecdysone. At time 0, ecdysone was added to the
dissected salivary glands, and it was present at a constant
concentration throughout the experiment. Note that the
intermolt puffs, present at the beginning of the experiment,
disappeared over the first two hours. The early puffs began to
appear after time 0, reached their maximum size at about 4
hours, and then regressed in size. The late puffs started to
appear at about 5.5 hours, reached their maximum size at about
10 hours, and then regressed. (Remember that all times are the
number of hours from the addition of ecdysone.)
Experiment (B) shows the response of Drosophila puffs to
ecdysone in the presence of cycloheximide. At time 0, both
ecdysone and cycloheximide were added to the dissected
salivary glands. Cycloheximide is an inhibitor of translation
(protein synthesis). This means that any protein present at the
beginning of the experiment is still active and that transcription
can still occur, but the cells cannot synthesize any new protein
during the course of the experiment. Note that there were no
changes in the intermolt puff response. The appearance of the
early puffs followed the same time course as in experiment
(A); however, the early puffs failed to regress. The late puffs
never appeared.
Experiment (C) shows the response of Drosophila puffs to a
brief exposure to ecdysone. At time 0, ecdysone was added to
the dissected salivary glands. After 2 hours, the ecdysone was
washed out of the salivary glands and removed, so it was no
longer present in the cells. Note that the early puffs
immediately began to regress in size after the ecdysone was
removed. Also note that late puffs were prematurely induced,
meaning that they began to appear after about 3 hours.
(a)
Briefly explain, in general, how the hormone ecdysone can cause changes in the
chromosomal puffing pattern. (5 qp)
(b)
List three specific transcriptional processes that are regulated directly by the
ecdysone-receptor/ecdysone complex. Briefly explain how the data demonstrate
that these processes are regulated by the ecdysone-receptor/ecdysone complex.
(15 qp; 2 qp for each process & 3 qp for each explanation)
(c)
Suggest an explanation for the observation that the early puffs do not regress and
the late puffs are not induced in the presence of cycloheximide. How could you
test your hypothesis? (5 qp)
4.
Distinguish between synaptic, paracrine, and endocrine mechanisms of cell
signaling. (5 qp)
5.
Cyclic AMP (cAMP) plays an important role as a second messenger in cell
signaling processes using G-protein-linked receptors. Therefore, it is important
for a cell to carefully regulate the intracellular concentration of cAMP. An
interesting illustration of the role that cAMP plays in the physiology of the whole
organism comes from studies of Drosophila melanogaster. There is a mutation in
Drosophila called dunce. Flies that are homozygous for dunce have a reduced
amount of an enzyme called cyclic AMP phosphodiesterase. In fact, dunce flies
have only about half the amount of cAMP phosphodiesterase as normal wild-type
flies. Cyclic AMP phosphodiesterase acts to break down cAMP, reducing its level
in the cells. Researchers developed a learning test in which flies were presented
two metallic grids, one of which was electrified. If the electrified grid was painted
with a strong-smelling chemical, normal flies learned quickly to avoid the grid
even when it was no longer electrified. Mutant dunce flies, on the other hand,
never learned to avoid the smelly grid.
(a)
Assume that Drosophila cells have a similar mechanism for the regulation of
glycogen metabolism as mammalian cells, and that Drosophila cells are capable
of responding to epinephrine in a manner similar to mammalian cells. In separate
experiments, cells from either wild-type or dunce flies were treated for a short
time with epinephrine; then, the epinephrine was removed. The rates of glycogen
synthesis and glycogen breakdown were measured at timed intervals after the
epinephrine treatment. How would dunce cells differ from wild-type cells?
Briefly explain your answer. (5 qp)
(b)
Caffeine is a phosphodiesterase inhibitor. What effect do you predict that caffeine
would have on the learning performance of normal, wild-type flies. Briefly
explain your answer. (5 qp)